A detection and ranging apparatus transmits a probe signal and receives an echo signal generated in such a way that the probe signal is reflected by the target which is a detection target. The detection and ranging apparatus thereby detects a target and measures a relative distance in an eye direction (hereinafter referred to simply as a “distance”) up to the target and a relative velocity in the eye direction (hereinafter referred to simply as a “velocity”) of the target. Examples of the detection and ranging apparatus include a radar apparatus that transmits a radiowave as a probe signal. Such a radar apparatus can be mounted in an automobile and the like. Assume that a target identified by the detection and ranging apparatus is distinguished according to a number k (k=an integer equal to or larger than 1) and a kth target moves in a position by a distance dk from the detection and ranging apparatus at a velocity vk. At this time, a propagation delay Tk from the detection and ranging apparatus to each target, and a Doppler frequency ωdk for the detection and ranging apparatus with regard to a carrier angular frequency (hereinafter referred to simply as a “frequency” unless otherwise misunderstood) ωc, and a light velocity c0 are respectively represented by the following expressions (1) and (2).
                              τ          k                =                              2            ⁢                          d              k                                            c            0                                              (        1        )                                          ω          d          k                =                              2            ⁢                          ω              c                        ⁢                          v              k                                            c            0                                              (        2        )            
In an environment where a plurality of the above described detection and ranging apparatuses are present, the detection and ranging apparatus may receive a signal transmitted from a different apparatus as an interference signal in addition to an echo signal from a target. Accordingly, to accurately perform the above described detection and measurement, the detection and ranging apparatuses need to detect a signal (interference signal) transmitted by the different apparatus from a reception signal, to suppress the detected interference signal, and to preferably remove the interference signal. FIG. 1 illustrates an example of a situation where interference occurs between detection and ranging apparatuses.
Radars 1 and 2 illustrated in FIG. 1 are one example of the detection and ranging apparatus. The radars 1 and 2 are radars that use, for example, a probe signal modulated with a Frequency Modulated Continuous Wave (FMCW) method, or a probe signal modulated with a Direct Spectrum Spreading Signal (DSSS) method. The radar 1 transmits a probe signal by using a transmission antenna AT1, and receives an echo signal from a target TD by using a reception antenna AR1. Moreover, the radar 2 transmits a probe signal by using a transmission antenna AT2, and receives an echo signal from the target TU by using a reception antenna AR2.
As described above, the radar 1 receives, via the reception antenna AR1, an echo signal (desired signal) vRXD(t) generated in such a way that the probe signal transmitted via the transmission antenna AT1 is reflected by the target TD. Then, the radar 1 detects the target TD based on the received desired signal vRXD(t), and measures feature amounts such as a distance to the target TD and a velocity of the target TD. However, as illustrated in the example illustrated in FIG. 1, the radar 1 can possibly receive, via the reception antenna AR1, a signal (interference signal) VRXU(t), which is generated in such a way that the probe signal transmitted via the transmission antenna AT2 of the radar 2 is reflected by the non-target TU, along with the desired signal VRXD(t). The superscript “(D)” represents “Desired”, whereas the superscript “U” represents “Undesired”. Assuming that an additive white Gaussian noise is n(t), the signal v(t) received by the reception antenna AR1 is represented by the following expression (3).v(t)=vRXD(t)+vRXU(t)+n(t)  (3)
In order that the radar 1 may accurately measure the feature amounts of the target TD, it is desired to remove an undesired signal VRXU(t) from a reception signal v(t) in the expression (3).
An interference detecting apparatus for use in a radar apparatus, which randomly changes set channels of output signals at certain timing and detects an abnormality caused by interference based on a plurality of measurement results in the changed different channels, is known.
Additionally, an FMCW radar that transmits a radar wave using a frequency different from an interference wave by changing a central frequency of a voltage control oscillator when an absolute value of a change amount of sampling data obtained by sampling a beat signal is larger than a set threshold value is known.